Move demos in ColunaDemos.jl

[guimarqu]

Fixes issue #73

[codecov-io]

Codecov Report

Merging #76 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #76   +/-   ##
=======================================
  Coverage   83.68%   83.68%           
=======================================
  Files          33       33           
  Lines        1477     1477           
=======================================
  Hits         1236     1236           
  Misses        241      241

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[vitornesello]

Need to remove the directories test/models/ and examples/ from Coluna.
Also, add to ColunaDemos.jl the function to check the gap solutions. This function is written in examples/GeneralizedAssignment_SimpleColGen/run_sgap.jl